Associated Press WriterNEW YORK (AP) -- A explosion rocked a 10-story commercial building Thursday, spraying glass and rubble across a quiet block and injuring up to 50 people, authorities said.

"It was a giant boom -- a real giant boom," said neighborhood resident Bill Beek, who lives a half-block away. "It sounded like an airplane crashing."

Several victims, at least three in serious condition, were taken to four Manhattan hospitals for treatment. One hospital, St. Vincent's, said it was treating eight patients, six of whom were critically injured. Other victims, bloody and bandaged, sat on curbs waiting for transportation.

A preliminary injury total stood at 50, said police spokesman Michael O'Looney. A tally of hospitals showed at least 20 people were taken to four of them; other people were treated at the scene.

Plumbers were working on the boiler in the commercial building at 121 W. 19th St. at the time of the 11:30 a.m. blast, but it was unclear if that was the cause of the explosion.

Windows along the block were blown out by the force of the blast, and several of the injured were hit by flying glass. The facade of the building was blown off; it was unclear how much of the building's interior had collapsed.

Scott Bonilla, a student at the nearby Apex Technical School, said he was inside the building when it began shaking.

"They told us to rush out of the building," he said. "There was like an explosion ... and I ran out of there."

Law enforcement officials said did not appear to be an act of terrorism.

"It was just a really loud noise," said Stuart Markowitz, who runs the technical school's education department. "Some of our windows did get blown out."

All students were safely evacuated, he said. Initial reports that the explosion took place inside the school itself were not true, he said.

Sid Dinsay, a spokesman for the city Office of Emergency Management, said the building housed commercial tenants including a sign company.

Power was cut off to two buildings on the block at the request of the Fire Department, and officials asked for voluntary evacuation of the rest of the street.

More than 100 firefighters were called to the scene.